Production of artificial filaments and other materials



United States Patent PRODUCTION OF ARTIFICIAL FILAMENTS AND OTHER MATERIALS Nicolas Drisch and Paul Herrbach, Paris, France, assignors to Textile & Chemical Research Company Limited, St. Peter Port, Guernsey, Channel Islands No Drawing. Application May 11, 1958, Serial No. 354,419

.Claims priority, application France August 26, 1952 5 Claims. (CI. 18-54) This invention relates to the production of artificial filaments, yarns, fibres, films and other continuous lengths of material having a basis of cellulose triacetate. The foregoing materials will be hereinafter referred to generally as filaments and the like.

Cellulose triacetate, by which is meant cellulose acetate having an acetyl content of 60 to 62.5% (calculated as acetic acid) is \commonly prepared by the acetylation of cellulose, e. g. by means of aceticanhydride in the presence of sulphuric acid as a; catalyst. Processes have been described wherein the primary solutions of cellulose triacetate so obtained are neutralized or stabilized to neutralize the residual sulphuric acid or are otherwise treated to reduce the sulphuric acid content and are then used directly for the spinning of artificial filaments and the like.

It has now been discovered that, providing the spinning conditions are suitably selected, such primary cellulose triacetate solutions may be spun to form very satisfactory filaments and the like without recourse to any prior treatment to eliminate the sulphuric acid catalyst.

According to the present invitation a process for the production of artificial filaments and the like materials comprises spinning a primary cellulose triacetate solution formed by the acetylation of cellulose in the presence of sulphuric acid as catalyst, without neutralization or elimination of the sulphuric acid, into a bath of dilute acetic acid below a temperature of 25 C.

- In the preferred form of the invention the cellulose triacetate employed has a degree of polymerisation of 250 to 500, e. g. 350 to 400. The concentration of cellulose triacetate in the spinning solution is preferably 8 to 14% and most advantageously 11 to 12%. The viscosity of the spinning solution is preferably 500 to 1500 poises and most advantageously 600 to 800 poises.

. The un-neutralised primary cellulose triacetate solution is unstable on warming and should for, preference therefore be maintained at a temperature below 20 C. continuously from its production to its spinning.

. The spinning bath of dilute acetic acid is preferably of a concentration of 150 to 300 g./litre and the spinning temperature is below 25 C. and preferably to 15 C.

The bath is preferably circulated either co-current or counter-current to the spun filaments.

The spinning process takes placevery easily and without obstruction or adhesion of the fibres, especially when the preferred conditions set out above are employed, despite the very high initial swelling of the coagulated filaments Which may be as large as 300 to 400%' It is believed that the sulphuric acid present, which ionises in the spinning bath, has an important effect on the physical characteristics of the filaments obtained since, despite the high initial swelling of the fibres (which usually results in products which are rather rough to the touch), the products obtained after thorough washing and drying are soft and silky to the touch even without the application of any lubricant thereto. I

It'is preferred, in accordance with the invention, that 2,768,870 Patented Oct. 30, 1956 the filaments produced should be subjected to stretching, e. g. to the extent of 50 to immediately after they leave the spinning bath. The filaments after stretching, if that step is employed, should be carefully washed to remove residual acetic acid and any traces of sulphuric acid remaining in them. Washing may be effected by passing the filaments through hot water at, for example, to C., and this treatment, especially at the higher temperatures, substantially reduces the swollen condition of the filaments, e. g. from 300% down to 100%. The filaments are then preferably wound on open supports or cut to short fibres and are then re-washed in hot water until the washing water shows no acid reaction when tested by the usual coloured indicators. The filaments or fibres are then preferably dried without tension.

The used spinning bath may be passed to an appropriate plant for recovery of the acetic acid.

The filaments and like products so obtained consist of cellulose triacetate having an acetyl content of 60 to 62.5 and preferably 615 to 62% and contain at most only very slight traces of sulphuric acid. They have a tenacity of 1.2 to 2.0 g./ denier when dry and 0.7 to 1.6 g./denier when wet. When they are heated for 7 days at C. the filaments do not discolour and their tenacity is lowered by only a few percent, generally less than 5%, these facts indicating the stability of the products. The filaments brown or decompose at 310 to 330 C.

The following is a description of the general conditions which are preferred in carrying out this invention.

Wood pulp, having a degree of polymerisation of 1050, is heated with an equal weight of glacial acetic acid and allowed to stand for 45 minutes. Acetic anhydride and traces of sulphuric acid (for example 0.75% calculated on the a-cellulose present) are then added in order to take up the water present in the pulp. After about half an hour, the reaction is complete. These two operations are carried out at low temperature, for example 8-l0 C. There is then added a mixture of:

700 cc. of glacial acetic acid 340 cc. of acetic anhydride 5 cc. of sulphuric acid to 100 grams of dry pulp, the mixture being cooled to 5 C. The mixture is then maintained for 2 hours at 1835 C. and for 2 more hours at 3538 C. It is then cooled and the required quantity of water, in the form of 60% acetic acid, is added to hydrate the residual acetic anhydride. The sulphuric acid is not neutralised.

The foregoing is but an example of a method of acetylation; the quantities of reactants employed may be varied within fairly wide limits provided that the time of reaction and the reaction temperature be suitably adjusted. Such a solution, however, is sufficiently stable with regard to its viscosity, its degree of polymerisation and the acetic acid content of the triacetate if it is kept below 20 C. or preferably at 18 C.

The solution is clear and readily filterable (filtration constant K of the order of 100), and contains l1.5-12% of cellulose triacetate. However, concentrations of 8 44% may be obtained by varying the conditions of preparation.

The'viscosity at 18 C. may similarly vary from 500 to 1,500 poises, but lies between 600 and 800 poises under the above conditions. The degree of polymerisation of the cellulose regenerated from the triacetate may vary between 250 and 500, and under the above conditions it is 270 to 330.

The primary solution may' be spun by conventional equipment for spinning viscose yarns into an aqueous bath containing 300 g./l. of acetic acid. The optimum should be reduced for higher speeds in order to accelerate the coagulation. The bath is preferably maintained at 15 C.

By reason of the nature of the solutions employed, the supply pipes and the swan-necks must consist of materials resistant to these solutions, such as stainless steel or unplasticised polyvinyl chloride.

The spinning and stretching do not present any difficulty, and the washing, while being lengthy as already stated, is also not diflircult. The products may be dried by conventional methods.

' Filaments can be obtained which have tenacities of 1.02.0 g./denier in the dry state, and O.71.6 g./denier when wet, depending upon the degree to which they have been stretched. The elongation of the filaments is of the .order of 1030% according to the stretch which has been applied. The relative loop strength is 8085% for high elongations, and 6570% for smaller elongations. Secondary swelling of the product is low (about but, nevertheless, dyeing is simple. However, if desired, the yarn may be dyed before the primary swelling has been wholly removed by drying.

The appearance of the filaments is silky and lustrous, as already stated. Dyeing with all the dyes usually employed for cellulose acetate is simple, and bright and full tones can be obtained. It has been observed that the speed at which the dyes are taken up is higher than in thecase of the secondary cellulose acetates, which suggests that a diiferent physical structure is present. Generally, the shades obtained are darker under comparable dyeing conditions.

De-lustering agents or pigment dyes may be added to the solutions in order to obtain yarns which are matt or dyed in the mass.

The individual filament denier of the fibres may vary considerably but, as is always the case, the thicker fibres are more diflicult to handle.

The following examples will serve to illustrate the invention:

Example I A 12.4% cellulose triacetate solution having a viscosity of 600 poises at 18 C. is spun through a spinneret having 60 apertures of 0.08 mm. diameter into a bath containing 175 g./litre of acetic acid at 12 C., with a travel of 50 cm. in the bath. The total count spun is 375 denier, giving 6.25 denier per filament.

The yarn is stretched by rolls outside the bath, the first roll delivering the yarn at the extrusion rate of the solution. The final spinning speed is 52 m./min.

The yarn is freed of adhering liquid after the stretching and is washed by passing it through a long tube in which water travels counter-current to the yarn. On leaving this tube, the yarn still contains few percent of acetic acid. It is wound on a bobbin and the wound package obtained, when removed from the bobbin, is washed by sprinkling with cold water for 24 hours, the final phase of the washing being effected with softened water. A size in soft water, to which a trace of bicarbonate may be added, is then applied. The wound package is dried without tension.

The yarn thus produced has the following character istics:

Tenacity:

Dry g./denier 1.82 Wet do 1.21 Elongation:

Dry percent 10.7 Wet do 14.3

The degree of polymerisation of the cellulose regenerated from the yarn is 350.

Example II A cellulose triacetate solution (11.9%) having a viscosity of 630 poises at 18 C. is spun by means of a spinneret having holes of 0.006 mm. diameter, so as to give a yarn of 500 denier per 100 fibres. The bath contains 170 g./l. of acetic acid and is at a temperature of 11 C. The length of travel in the bath is 50 cm.

The yarn is stretched by 30% outside the bath so that the final spinning sped is 41 m./min. The treatment is continued as above, but the washing takes place continuously on reels.

The characteristics of the yarn obtained are asfollows:

Tenacity:

Dry g./denier 1.22 Wet do 0.74 Elongation:

Dry "percent-.. 23.9 Wet do 30.5

The degree of polymerisation of the cellulose regenerated from the yarn is 280.

Example III By operating as in Example II, but imparting a stretch of 35% (final spinning speed 80 m./min.), a yarn is obtained which has tenacities of'1.5 and 0.9 g./ denier and elongations of 14.4% and 18.1%. The degree of polymerisation of the regenerated cellulose is the same.

Example IV The same conditions of preparation are applied as in Example II, but are artificial staple fibre spinneret having 3,500 apertures of 0.08 mm. is employed, with a spinning bath containing 280 g. of acetic acid per litre. A stretch of 60% is applied to obtain a final spinning speed of 55 m./min. The length of travel in the bath is 1 metre. After stretching the tow is cut into lengths of 40 mm. and the fibres are stacked in a perforated basket and 'subjected therein to a thorough washing with water. vAlternatively, the tow may be stacked in the basket and cut after washing or even after drying.

The fibres of 4.5 denier obtained have a dry tenacity of 1.89 g./denier and a wet tenacity of 1.42 g./denier for corresponding elongations of 10% and 12.8%.

The yarns and fibres produced are suitable for all textile uses, but the fibres are particularly suitable for blending with wool. It is desirable in the latter case to apply an appropriate anti-static oil.

The examples mention the use of spinnerets having from 60 to 3,500 holes. Experiments have also been made with the use of spinnerets having 40 holes and 8,400 holes with bores of0.06 to 0.08 mm. without the least difficulty having been encountered.

If the spinning solutions of this invention are poured on to plates, a polished drum or a travelling belt, thin films are produced. The coagulation takes place under comparable conditions. All the products obtained are characterised by a very low absorption of the humidity of the air and by a remarkable dimensional stability. The shrinkage on washing of the textile articles obtained from the yarns is practically nil. The low water-absorption rate also ensures rapid drying of these articles after washing.

We claim:

1. A process for the production of artificial filaments and films, which comprises acetylation of cellulose with a mixture of acetic acid and acetic anhydride in the presence of sulphuric acid as a catalyst, and hydration of the residual acetic anhydride, and extruding the thus obtained primary solution of cellulose triacetate in acetic acid, in the presence of residual sulphuric acid, into a bath of dilute acetic acid at a temperature below 25 C.

2. The process set forth in claim 1 in which the acetic acid bath contains to 300 g./ litre of acetic acid.

3. The process set forth in claim 1 in which the primary solution of cellulose triacetate contains 11 to 12% of cellulose triacetate.

4. The process set forth in claim 1 in which the primary solution of cellulose triacetate has a viscosity of 500 to 1,500 poises.

5. The process set forth in claim 1 in which the formed product is stretched 50 to 75% continuously with its production.

References Cited in the file of this patent UNITED STATES PATENTS Johnson et a1 Nov. 3, 1953 

1. A PROCESS FOR THE PRODUCTION OF ARTIFICIAL FILAMENTS AND FILMS, WHICH COMPRISES ACETYLATION OF CELLULOSE WITH A MIXTURE OF ACETIC ACID AND ACETIC ANHYDRIDE IN THE PRESENCE OF SULPHURIC ACID AS A CATALYST, AND HYDRATION OF THE RESIDUAL ACETIC ANHYDRIDE, AND EXTRUDING THE THUS OBTAINED PRIMARY SOLUTION OF CELLULOSE TRIACETATE IN ACETIC ACID, IN THE PRESENCE OF RESIDUAL SULPHURIC ACID, INTO A BATH OF DILUTE ACETIC ACID AT A TEMPERATURE BELOW 25* C. 